Enhancement of the photo catalytic performance of TiO₂ catalysts via transition metal modification

The physicochemical properties and photo catalytic activity of transition metal-loaded TiO₂ catalysts were studied. The transition metal was deposited on TiO₂ via post-hydrothermal synthesis and photo-assisted reduction/impregnation. The structure of TiO₂ is preserved upon adding Pd, Cr, and Ag into it. Nevertheless, the structure of TiO₂ was destroyed when reacted with silicotungstic acid (Si-W). As a consequence, under the irradiation of visible light, the Pd and Cr loaded TiO₂ showed higher photo catalytic activity compared to pristine TiO₂ and Si-W loaded TiO₂ has no catalytic activity, although the threshold absorptions of all metal loaded TiO₂ is similar to that of pure TiO₂. Transition metal was homogeneously coated on the TiO ₂ particles and there is no phase separation between metal salts and TiO₂ as revealed with scanning electron micrographs (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD) data. X-ray photoelectron spectroscopy (XPS) spectra showed that all metals in metal loaded TiO₂ presented as an ionic state with slightly reduction compared to the metal in metal salt used in the reaction, probably due to the interaction with TiO₂. These results suggested that the crystallinity was important for the photo catalytic activity of TiO₂ based catalysts and the function of transition metal is to increase the electron-hole recombination time, therefore increase the catalytic activity.